It is well known to those skilled in the art that the lithographic printing process depends, in part, for its success in the ability of the ink to form a stable emulsion with an aqueous fount solution prior to the transfer of the ink to a printing plate and, for offset lithography, to a printing blanket. The Printing Ink Manual, 4th Edition (1988), published by Van Nostrand Reinhold (International) Co. Ltd. and The Lithographers Manual, 7th Edition (1983), published by The Graphics Arts Technical Foundation, Inc. both teach the equipment, procedures, and materials typically used in a lithography printing operation.
The general issues concerning achieving a good emulsification between the printing ink and the fount solution is described in W. Beier et al.: “Emulsifying of dampening solution in offset ink in short inking units”, 31st International Research Conference of IARIGAI, Copenhagen, Denmark. May 9-Aug. 9, 2004, Proc. page 65, Vol. 31) and Textile Research Journal, September 1981, Vol. 51, no. 9, pages 607-613.
It is well known to those skilled in the art that an emulsion may be made by incorporating water or predominantly aqueous media into a lithographic ink, for example, by high speed stirring together of the two components or by mixing in a Z-blade or similar mixer. However, such emulsions are not always stable. Further, it is also known to those skilled in the art that emulsifying agents used in too high a quantity can lead to overemulsification and thus to inferior print performance of lithographic inks, and can also render tacky the dried ink films after printing.
Improving the emulsifiability of lithographic inks in a conventional offset printing process is taught by U.S. Pat. No. 7,909,924 and by U.S. Pat. No. 7,985,820, both to Krishnan, et al., which disclose stable offset emulsion inks containing non-water soluble polymeric surfactants, useful as components of heatset printing inks.
In order to better provide for a stable emulsified lithographic printing ink system, so-called “single-fluid” or “self-dampening” inks have been developed, which incorporate water into the printing ink and, in conjunction with special waterless printing plates, attempt to obviate the need for a separate fount solution during the printing process. The ink/water emulsion must be stable during storage of the ink, and during the initial stages of printing, yet the water must be released from the ink during the final stages of printing in order that a satisfactory dry ink film be obtained. U.S. Pat. No. 7,240,615 to Lee et al. teaches single fluid lithographic inks containing glycerol for waterless lithography. WO 2004/041946 to Latunski et al. discloses single fluid lithographic printing inks containing a continuous phase and an emulsified phase. The emulsified phase contains water and a polyol. U.S. Pat. No. 6,140,392 to Kingman et al., also discloses single fluid printing inks suitable for waterless offset lithography, wherein the continuous phase includes an acid-functional vinyl resin and the discontinuous (emulsified) phase a polyethylene glycol. US2004/0013983 to Lee et al. teaches the importance of selecting a surfactant of the appropriate hydrophobicity hydrophilicity balance (HLB) for a stable emulsion in single fluid inks.
US2004/115561 to Laksin et al. discloses single fluid energy-curable inks, suitable for waterless lithography. WO2004/045863 to Battersby et al. discloses a planographic printing apparatus and method utilizing a single fluid lithographic ink and special pH-neutral plate cylinder.
It is also well-known to those skilled in the art that successful emulsification of a lithographic ink and a predominantly aqueous medium may require the usage of special emulsifying agents, both to achieve a good level of emulsified aqueous phase, and to maintain the stability of said emulsion. The above-mentioned references disclose polyols and polymeric acids as being useful in this regard. More recently, the incorporation of water into a lithographic ink not specifically designed to be utilized as a “single-fluid” ink has described in U.S. Pat. No. 8,013,034 to Harui et al., which discloses a method of incorporating water in an emulsified form into an offset printing ink, necessitating the use of both an emulsion stabilizer and a water-soluble polymer. Another novel emulsifying chemistry, based on maleated fatty esters and amides, is disclosed by Harui et al. in U.S. Pat. No. 8,013,033. One cited driver for the incorporation of water into a lithographic printing ink is to reduce the volatile organic content (VOC) of that ink. VOC is harmful to air quality and detrimental to the environment of a print shop, most especially to the printers who must operate the printing presses. Historically, some lithographic inks, for example web offset heatset inks, contain between 30 and 45% VOC. Another is to reduce the cost of the raw materials per unit weight of ink.
Inks suitable for lithographic printing also frequently include extenders or fillers as a component. Such materials, which include bentonite, montmorillonite and kaolin clays, calcium carbonate and other inorganic materials, are known to those skilled in the art as a means to reduce the amount of expensive pigments and colorants required in an ink to achieve a particular printing density. They are also of value in optimizing the rheological properties of an ink, to facilitate transfer and printability and minimize piling on the blanket or printing plate, misting and flinging. Traditional extenders and fillers are disclosed in The Printing Ink Manual—Leach, Robert; Pierce, Ray. Fifth Edition (1993), published by Blueprint (pages 191-5) describes typical fillers and extenders for lithographic inks U.S. Pat. No. 4,193,806 to Finlayson discloses organic ink vehicles containing an organophilic clay gellant made from a smectite-type clay and a quaternary ammonium salt. U.S. Pat. No. 4,981,517 and U.S. Pat. No. 5,137,568, both to Durham et al., teach the improved dispersion of extender pigments, in particular kaolin clays, in lithographic offset and letterpress inks, by treating them with quaternary ammonium salts. Ink transfer and related issues in lithographic printing are discussed in The Printing Ink Manual—Leach, Robert; Pierce, Ray. Fifth Edition (1993), published by Blueprint (pages 792-7).
The prior art demonstrates that there is a need for inks suitable for printing by lithography, and, in particular, offset lithography, to be available economically, in order to maximize the value of this print process. There is also a need to minimize the impact of lithographic inks on the environment, by minimizing both their VOC and migratable components that might subsequently produce taint in packaged goods. Recent studies conducted in Switzerland, at the Kantonales Labor Zurich, have found high amounts of mineral oil to have migrated from cardboard used as packaging materials, wherein that cardboard was made from recycle paper and board waste, notably newspaper waste, into foodstuffs. Newspaper waste contains the residues of the coldset inks used to print those newspapers originally, and coldset inks contain a high proportion of mineral oils, to facilitate their drying mechanism of setting into the paper substrate.
The prior art has focused on the inclusion of water or predominantly aqueous media into lithographic inks and, separately, on the inclusion of fillers and extenders into lithographic inks. There is further a need to improve constantly the performance of said inks as printing equipment becomes ever more sophisticated and is able to run with a shorter start-up time, at higher line speeds, and with a wider variety of substrates.
Further, the prior art has described emulsified offset inks under the concept of waterless printing or under the synonym self-dampening ink or single fluid lithographic ink, but only for inks which dry by aerial oxidation (so-called “sheetfed” inks), evaporation of solvent or absorption into the substrate (so-called “coldset” inks) or through the application of heat in the form of hot air or infra-red radiation (so-called “heatset” inks). There is a need to have the same benefits of emulsified lithographic inks with improved transfer available for those inks which cure through actinic radiation or by electron beams (so-called “energy-curing” inks). There is further a need to minimize the raw material cost of such energy-curing inks, given that the oligomers, monomers, and photoinitiators normally present as components of energy-curing lithographic inks are themselves expensive. Therefore there is a need to have available energy-curing inks wherein a stable water/ink emulsion is present without the need for emulsifying agents which can be expensive and render the dried ink films after printing and curing tacky.